Telephone system having preset transmitter



Dec. 19, 1950 L. J. BOWNE 2,534,850

TELEPHONE SYSTEM HAVING PRESET TRANSMITTER Original Filed April 4, 19458 Sheets-Sheet 1 FIG.

20 FIGSQ jg? m e a $3 s2 5/ 9% .1 @IQ 1 I g 2a P/ Q i x P3 P2 9-4 PO.236 o c /2/ lNVENTOR .1 BOW/V5 a; 1

' ATTORNEY Dec, 19, 11950 L. J. BOWNE 2,534,850

TELEPHONE SYSTEM HAVING PRESET TRANSMITTER Original Filed April 4, 19458 SheetsSheet 2 LJBOWNL K; 144* A 7' TORNEY Deca 19, 1950 L. J. BOWNE2,534,850

TELEPHONE SYSTEM HAVING PRESET TRANSMITTER Original Filed April 4, 19458 Sheets-Sheet 5 IN L E N TOR L.J.8OWNE A 7' TORNEV Dec. 19, 3.950 L..1. BOW-15E TELEPHONE SYSTEM HAVING PRESET TRANSMITTER 8 Sheets-Sheet 4Original Filed April 4, 1945 u 20k in a tot fin a kotim mmmwmmmm[NVENTOR L J. BOWNE 4 a Dec. 19, 1950 L. J. BOWNE TELEPHONE SYSTEMHAVING PRESET TRANSMITTER 8 Sheets-Sheet 5 Original Filed April 4, 1945wnhumvnuz P tot: Y

INVENTOR By. LJ BOWNE a a 4% ATTORNEY Dec. 19, 1950 J. BOWNE 2,534,850

TELEPHONE SYSTEM HAVING PRESET TRANSMITTER Original Filed April 4, 19458 Sheets-Sheet e n55. cxr. ran 3T4 TION "I INVENTOR L.J.80WNE [A rTORNEY Dec. 19, 1950 L. J. BOWNE 2,534,350

TELEPHONE SYSTEM HAVING PRESET TRANSMITTER Original Filed April 4, 19458 Sheets-Sheet 7 UVVENTOR L. JBOWNE 5):

ATTORNEY F Dec. 19, 1900 L. J. BOWNE TELEPHONE SYSTEM HAVING PRESETTRANSMITTER 8 Sheets-Sheet 8 Original Filed April 4, 1945 INVENTORL.J.BOWNE "14v? 761 Patented Dec. 19, 1 950 TELEPHONE SYSTEM HAVINGPRESET TRANSMITTER Langford J. Bowne, Saugerties, N. Y., assignor toBell Telephone Laboratories, Incorporated, New York, N. Y., acorporation of New York Original appiicaticn April 4, 1945, Serial No.586,560. Divided and this application October 17, 1947, Serial No.780,440

8 Claims. i

This invention relates to telephone systems and particularly to centralQfilCE, or private branch exchange telephone systems of the type inwhich subscribers stations, having normal access to the exchangeequipment in the extension of calls originated at the stations, areprovided with additional facilities whereby direct communicationconnections between the several stations of the system may be initiatedexpeditiously and with a minimum of effort on the part of thesubscribers thereat, and may be completed without routing the callsthrough the central office, or private branch exchange.

This application is a division of application, Serial No. 586,560, filedApril 4, 1945, now Patent 2,433,836, issued Jan. 6, 1948.

Systems of communication of the above-indi cated character are generallyknown as key calling telephone systems in that connections betweencalling and called stations of the system may be initiated at any of thestations by simply actuating a key, or button, at the calling stationassigned to the desired called station.

It is the object of this invention to provide an improved telephonesystem of the key calling type.

This object is attained in accordance with a particular feature of theinvention by characterizing each of a plurality of station-identifyingcode signals by a different combination of three current impulses ofpositive, and/or negative polarities, and by the provision of presetmeans at the subscribers station for predetermining the character ofeach of the three code impulses, and

of means which function, incident to the removal of the telephone fromits support at the calling station, to consecutively transmit theprecharacterized impulses over the calling line to control thecompletion of a connection from the calling station to the calledstation identified by the consecutively transmitted code impulses.

More particularly, this feature of the invention contemplates a codesignal transmitter of the dry rectifier type, and means embodied thereinand selectively controlled by any of a plurality of manually operablestation-identifying keys, or buttons, for preparing the transmitter forthe transmission of a preselected code corresponding to the operatedkey, and other means for rendering the transmitter operable, to transmitthe preselected code, in response to the removal of the telephone fromits support subsequent to the actuation of the code selecting key, orbutton.

Another feature of the invention contemplates facilities whereby a falseor incorrect setting of the code transmitter may be corrected prior tothe removal of the telephone handset from its support at acal1originating station.

A further feature of the invention provides facilities wherebyconference connections may be originated at any of the stations of thesystem, or additional stations may be added to an al ready existingconnection between two stations without the necessity for theoriginating, or adding subscriber to restore the telephone to its sup-'port. More particularly, during the existence of a connection betweenany two subscribers stations, either subscriber may actuate a key, orbutton corresponding to a third station to prepare the transmitter atthe station for the transmission of the code signal which identifies thethird station, and then operate key means which simulates the removal ofthe telephone at the station in causing the transmitter to operate andtransmit the code of the third station.

A still further feature of the invention resides in the provision ofmeans whereby a connection extending from any station and involving acentral ofiice or private branch exchange line may be held bytransmitting from the station a predetermined code signal. Moreparticularly, a hold key is provided at each of the stations andfunctions to transmit a predetermined group of code impulses whichselectively control the connection of a holding bridge to the centraloffice, or private branch exchange line.

Still another feature of the invention provides facilities whereby asubscriber may hold a con-- nection on a central ofiice, or privatebranch exchange line, and thereafter selectively complete acommunication connection between his station and any other station ofthe system, and may also be a party to a conference connection for theperiod during which the central office, or private branch exchangeconnection is held.

Another feature of the invention precludes the possibility of losing acentral oflice, or private branch connection in the event of accidentaloperation of the switchhook contacts after a call to the central ofilceor private branch exchange has been initiated.

Other features of the invention contemplate novel circuit arrangementswhich render possible the realization of the features individually setforth above. In accordance with one such other feature, a pyramidalarrangement of selectively operable line-connecting relays is resortedto, the relays of which function under control of the code transmittersat the several stations of the system to selectively interconnect theline 3 circuit of any calling station and the line circuit of any of aplurality of called stations. More particularly, each of the relays ofthe pyramidal arrangement of line-connecting relays comprises twoseparately energizable windings, each of which is selectivelycontrollable from one of two different stations to extend a calling lineto a called line. Each double winding line-connecting relay is assignedto two stations and is controlled therefrom in such a manner that when afirst station originates a call to a second station the relay operatesover one winding incident to the operation, at the first station, of akey, or button, allocated to the second station, and when the secondstation originates a call to the first station the relay operates overits other winding incident to the operation, at the second station, of akey, 01' button, assigned to the first station, and when operated overeither winding, functions to interconnect the line circuits of bothstations. Thus, the number of line-connecting relays for a systeminvolving a predetermined number of stations is determined by theformula where n is the predetermined number of stations. For example, ina system involving eighteen stations, the number of line-connectinrelays required is one hundred fifty-three.

A still further feature of the invention contemplates the signaling of9. called station substantially instantaneously with the seizure of thecalled line and to thereafter continue signaling the called station onan intermittent basis. This feature is obtained by means of a ringingcontrol circuit comprising a single relay, a. resistance and athermistor, and a local source of alternating current, the elements ofthe ringing control circuit being so disposed relative to one anotherthat, upon the operation of the relay to connect the alternating currentsource to the called line, the resistance is connected in parallel withthe thermistor and the relay winding to reduce the current flowingthrough the thermistor. The thermistor accordingly cools oii so as toprevent sufiicient current to traverse the relay winding. The relay thenreleases and opens the resistance shunt thereby permitting sufficientcurrent to again traverse the relay winding through the thermistor tocause the relay to operate. This cycle of operation and release of theringing relay is repeated and the alternating current source isintermittently connected to the called line in a manner that simulatesmachine ringing and precludes the delay in the operation of the ringerat the called station which occurs when the ringing relay operates onthe silent interval.

These and other features of the invention will be best understood fromthe following detailed description when read. in connection with theaccompanying drawings, in which:

Fig. 1 is a perspectiveview of a telephone set illustrating the locationof the various reset, hold and station-selecting buttons thereon. Ifdesirable, the reset and hold buttons may occupy positions other thanthose illustrated, for example, the reset button may be located on oneside of the set and the hold button to the right or left of the dial;

Fig. 2 is an end view of the telephone set showyi in Fig. l with aportion of the side wall of the casing broken away to expose the transmitter mechanism housed within the casing. In

this view the mechanism is depicted in its normal condition and with thetelephone handset on its cradle support;

3 is a View similar to that of Fig. 2 showing one of the buttonsdepressed and the handset partially lifted from its support;

Fig. 4 is a fragmentary view of the transmitter control mechanism whichis operated incident to the removal of the handset from its support. Inthis View the handset has been completely removed from its support;

Fig. 5 is a plan view of the code transmitter mechanism;

Fig. 6 is a view of the reset control mechanism prior to the operationof the reset button;

6A is a. view similar to that of Fig. 6 showingthe reset controlmechanism in its operated condition;

Figs. 7 and 7A are views illustrating the mannor in which the buttonsare mounted, and the latching and releasing mechanisms therefor;

Fig. 8 is a detail view illustrating the means employed for maintainingthe code transmitter cam shaft in its normal position and for insuringthe shaft coming to rest in that position aiter its cycle of operation;

Fig. 9 is a chart showing the various codes resulting from the operationof the buttons, and the bar contacts whose operation determines thecode;

Fig. 10 is a wiring diagram illustrating in si 1.- plified schematicform the line-connecting and control circuits involved in thekey-telephone system of this invention;

Figs. 11, 12, 13 and 14, when assembled in the manner indicated in Fig.15 constitute a detailed disclosure of the circuits involved in thekeytelephone system of this invention; and

Fig. 15 is a block diagram showing the manner in which Figs. 11, 12, 13and 14 are to be assembled to efiect a complete showing of the circuitsinvolved in the system of this invention.

Before entering into a detailed description of the code transmitterutilized at the several stations of the telephone system of thisinvention illustrated in the drawings and of the operation of thesystem, a brief reference will be made to Figs. 11 and 10 of thedrawings. Fig. 11 includes a schematic illustration of the codetransmitting mechanism while Fig. 10 is a schematic wiring diagramshowing in simplified form an over-all picture of the system.

The essential elements of the code transmitter are schematicall shown inFig. 11. It consists of a rotatable cam shaft 2G3 having fixed thereto,in spaced relation, three pulsing cams PI, P2 and P3; 3. pulse on camPO; an ofi normal cam PON; a single-toothed ratchet wheel or disc 22l;and a cam 23'! having a portion of its periphery flattened to cooperatewith a flat spring 236. The cam 23? and its associated spring 23!;function to assure the cam shaft coming to rest in its normal positionafter operation, and to hold it in this position. The left end of camshaft 203 is hollow so as to acconnnodate a projection of the gear wheelmeshing with a geared sector 255. A motor spring 262 has one end fixedto the gear wheel and the other end fixed to the ratchet wheel 225. Thecam shaft 2S3 is normally held against rotation by the pawl 228 whichengages the single tooth of the disc 22L When the eared sector 2! 9 isactuated in a manner to be subsequently described, energy is stored inthe motor spring 202, and when the handset 206 is removed from itsmounting, the

linkage shown between the handset button 286 and the pawl 220 functionsto disengage the pawl from the disc 22l whereupon the cam shaft 263makes a complete revolution under the action of the motor spring 2%.

The ofi normal cam PON is provided with a single notch whichaccommodates the stud controlling the contact springs SON when the camshaft is in its home position. The cam PO is provided with four notches,i, 2, S and the home position notch, spaced Bil degrees apart on the camperiphery. Each of the cams Pi, P2 and P3 is provided with a single camlobe, the three lobes being respectively displaced 90 degrees so thatthey function in sequence to operate their respective pulsing springsSi, S2 and S3. The springs SI normally maintain a group of two dryrectifiers a and b short-circuited on the transmitter side; the springsS2 normally maintain a second group of two dr rectifiers c and dshort-circuited on the transmitter side; and the springs S3 normallymaintain a third group of dry rectifiers e and f short-circuited on thetransmitter side. The two rectifiers of each group are oppositely poled.

Each of the dry rectifiers a, b, c, d, e and is normally, individuallyshort-circuited on the key selector side by corresponding springs A, B,C, D, E and F, which are individually controlled by the code bars Al,Bi, C2, D2, E3 and F3, respectively, which code bars, in turn, areoperated in various combinations under control of the keys, or buttons,designated H and 2 to it, inclusive. The combination in which the codebars are operated in response to the actuation of any of the keys, orbuttons, is indicated by the small circles appearing at the points atwhich the code bars cross the lines extending from the keys. Forexample, when key, or button, 9 is actuated, code bars Ai, D2 and F3 areactuated, in turn opcrating springs A, D and F. Thus, when any one keyor button, other than the reset button RE is actuated, one or more ofthe dry rectifiers has its individual short circuit removed by theoperation of the corresponding springs A, B, C, etc.

As the cam shaft 283 starts its clockwise rotation under the action ofmotor spring 262, the springs SON immediately are operated toshort thetelephone equipment and to connect the tip conductor of the station lineL to the ring conductor thereof through the springs S1, S2, S3 and SO,though the last set of springs, also operating at the start of rotationof the cam shaft, renders this connection open. When the cam shaft hasrotated 90 degrees, the lobe of cam Pi functions to separate the springsSi and simultaneously, the stud associated with the springs S0 dropsinto notch i of cam PO. At this interval, therefore, the circuit fromthe tip conductor of the line L extends through the alternate contactsof springs 259i and SON, conductor 223, through rectifiers a and b ifboth springs A and B are actuated, or through both springs A and B ifneither is actuated, conductor 222, springs S2, S3 and S0, to the ringconductor of line L. Thus, in the first signaling position of shaft2533, either one or the other, or both rectifiers a, b are effectivelyincluded in the signaling circuit involving the conductors of line L anddetermine the character of the impulse transmitted thereover during thisinterval.

As the shaft 253 moves out of its first position, the stud associatedwith springs Si functions to reclose the springs while the studassociated with springs SO moves out of the notch I in cam 6 PO to openthe springs SO. Thus the-signal transmitting circuit is restored to itsoriginal condition, that is, with all dry rectifiers short-circuited onthe transmitter side and the signal path open at the springs SO. In thesecond position of the cam shaft 263, the springs S2 are opened and thesprings SO are closed so that the character of the signal impulsetransmitted is determined by which, if any, or both of the rectifiers cand d have their short circuits removed by springs C and D. Similarly,for the third position of the cam shaft 2%, the springs S3 func-- tionto remove the short circuit from the third group of rectifiers e and 1,so that, an impuise, depending for its character upon whether or not anyof the two springs E and F is actuated, will be transmitted over theline L. The cam shalt comes to rest in its home position and the stationcircuit is reconnected to the line and the transmitter effectivelydisassociated therefrom.

The character of the code impulses consecutively transmitted by thetransmitter incident to the actuation of the keys or buttons El, 2 toH3, inclusive, and the corresponding operated code bar contacts, areshown in the chart of Fig, 9.

The key or button designated BE in Fig. 7 is a reset button and itsfunction will be described in detail hereinafter.

Fig. 1 discloses five subscribers stations each of which is equippedwith a telephone handset on the base of which are mounted eighteenbuttons or keys. In this showing only eighteen buttons are shown as amatter of convenience. The single heavy line conductors are intended torepresent the tip and ring conductors, or the communication channelsextending from each station and which are adapted for interconnection bythe various double winding line-connecting relays shown. The rectanglesdesignated REG are intended to represent the signal receiving andregister circuits individually associated with each station.

Extending from each rectangle REG are eighteen conductors which,incident to the actuation of the buttons H and 2 to is, inclusive, atany station are grounded to complete an energizing circuit for one orthe other windings oi the line-connecting relays, such as relays 2M,252, 253, 352, 348 and 315i. Relay 24! is common to both stations Nos. land 2, its upper i-2 winding being controlled by button No. 2 at stationNo. l and finds battery in the line circuit No. 2, so that whenenergized by way of its upper winding, relay 2M functions tointerconnect line circuits Nos. 1 and 2, with station No. I being thecalling station and station No. 2 being the called station. Similarly,the lower 2l winding of re lay 254 is controlled by button No. I atstation N0. 2 and finds battery in the line circuit No. I, so that whenenergized by way of its lower winding, relay 2d! again functions tointerconnect line circuits Nos. t and 2, with station No. 2 being thecalling station and station No. i being the called station.

Each of the other double wound pyramidal line-connecting relays issimilarly common to two stations, relay 252 being common to stationsNos. l and 3; relay 253 to stations Nos. 5 and relay 3352 to stationsNos. 2 and 3; relay 3% to stations Nos. '2 and i; relay 33! to stations3 and 4, etc. As will appear from a later description, the operation ofany line-connecting relay will be followed by the operation ofcorresponding cutthrough relays such as relays 228, 2 23, 322, etc.

Extending from each register circuit REG is a conductor designated X.This conductor is grounded incident to the actuation of the hold buttonor key at each station, that is, the lead X from the register circuitREG associated with station No. I will be grounded when the hold buttonH at station No. I is actuated; the lead X from the register circuit REGassociated with station No. 2 will be grounded when the hold button H atstation No. 2 is actuated; etc. The grounding of any of these leads willserve to operate a relay in the hold circuit, such as relay 580 of Fig.13 which functions to place a hold condition on the central ofiice, orprivate branch exchange line, as will be fully described hereinafter.

Normally, the line extending from each station is extended to thecentral office, or private branch exchange line over back contacts ofcorresponding cut-through relays 225, 2 33, 322, etc. so that when thetelephone handset at a station is removedfrom its support without astation-selecting buttonhaving been previously operated, the connectionis made in the usual manner through the central ofiice, or privatebranch exchange.

While but five stations are shown in Fig. 10, it is to be understoodthat the station capacity of the system is not so limited.

The description immediately following is directed to the mechanicalstructure of the codetransmitting mechanism, and for this purposeparticular reference is made to Figs. 1, 2, 3, 4, 5, 6, 6A, 7, 7A and 8.

The base of the telephone set is identified by the numeral and supportsthe cover or casing 2! in the well-known manner. Near the rear of thebase 20 and secured thereto by means of screws 22 is a mounting bracket23. This bracket is provided with a plurality of inwardly projectingarms 24 25, 25 and 2'! as clearly disclosed in Fig. 5. These armsconstitute supports for two shafts 28 and 20, the latter beingrelatively short and supported in suitable apertures in the bracket arms25 and 26. The shaft 28 which is considerably longer than shaft 29 issupported in suitable apertures in the bracket arms 24 and 2? and, asshown in Figs. 2 and 3, is located above and slightly forward of shaft29. The elements which are carried by these shafts and their functionswill appear as the description progresses. These shafts are preventedfrom longitudinal shifting by means of lock rings carried therebyexternally of the supporting bracket arms.

A pair of brackets 30 and 3! which occupy positions at right angles tothe longitudinal span of bracket 23 are fixed to the base 20 by means ofscrews 32 and each is provided with two vertically-extending armsindicated by the numerals 33, 34, and 35. Between the bracket arms 34and 35 is mounted a two-piece shaft, the two portions of which aredesignated by the numerals 3! and 38, respectively. The shaft 38 isrelatively long and at its inner, or left end viewing Fig. 5, isprovided with a relatively short axial bore into which the right end ofthe shaft portion 31 is adapted to be journaled for rotational movementrelative to the shaft portion 38. The shaft portions 3'! and 38 are alsoprovided with lock rings 40 and with fixed collars 44 to preventlongitudinal shifting thereof.

The shaft 3! supports a pinion gear 4!, a ratchet wheel 42 and a disc 03all of which elements are free to rotate on the shaft. The pinion 4! andthe ratchet wheel 42 are integrally formed so that any rotationalmovement experienced by the pinion is similarly experienced by theratchet wheel. The rotational movement of pinion 4! and ratchet 42 inone direction is communicated to the disc 43 through the pawl 45, which,as clearly shown in Figs. 2 and 3, is pivotally carried by the disc neara point at its edge and is biased in the direction of the ratchet wheelby means of the spring 46. Thus when the ratchet wheel 4! is driven in acounter-clockwise direction under control of a geared sector 2l9, aswill be described more fully hereinafter, the disc 43 is similarlyrotated.

The disc 43 is spring-coupled to the gear 22! by means of a motor spring202, one end of which is fixed to the disc 43 and the other end of whichis fixed to the gear 22!. The gear 22! is provided with a collar orflange which is pinned to shaft 38 so as to fix the gear thereto. Atripping pawl 220 is carried on the shaft 29 and is held in engagementwith the single tooth of the disc 22!. The pawl 220 is an integralextension of a substantially U-shaped member 60, the two inwardlyprojecting arms of which are apertured to permit the passage of shaft 29therethrough. A spring 6! whose ends bear respectively on the bracketarm 26 and the right arm of the pawl member 00 serves to normally biasthe pawl 220 in a direction such as to insure engagement of the pawlwith the gear 22!.

In the normal position of the code-transmitting mechanism as shown inFig. 2, the gear or disc 22! is held against counter-clockwise rotationby the influence of the pawl 220 so that when the sector 2!9 is actuatedto drive the pinion 4!, the disc 43 rotates, carrying with it one end ofthe motor spring 202, the other end of which is fixed to disc 22!, andsince the disc 22! is restrained from rotating by pawl 220, the motorspring 202 is wound up and stores sufficient energy to drive the shaft38 when the pawl 220 is tripped in a manner to be described hereinafter.

The shaft 28, which hereinbefore has been described as being mounted insuitable apertures in the bracket arms 24 and 21, pivotally supports asubstantially U-shaped member 52 having two depending arms 53 and 54,the former being considerably longer than the latter, as clearly appearsin Figs. 2 and 3. On the outer face of arm 54 is pivotally mounted aspring-biased latching pawl 55 which serves as a latch to maintain thegeared sector 2l9 in its operated position, as shown in Fig. 3. When thegeared sector 219 is raised to its operated position, the free end ofthe latching pawl 55 is forced by the action of spring 56 into the notch5'! on the inner peripheral edge of the sector 2l9 and holds the sectorin its operated position.

As will be described presently, the pawl member 00 with itsintegrally-formed pawl 220 is tripped to effect the release of the disc22! under two conditions, one in response to the removal of thetelephone handset 200 from its support, and the other in response to theoperation of the reset button RE. Similarly, the pawl 55 which functionsto lock the geared sector 2!9 in its 0perated position is actuated torelease the sector at a predetermined time in the operation of the codetransmitter. This release operation of the pawl 55 occurs near the endof the code-transmitting period and is effected by the engagement of acam with the lower end of the arm 53 as will be described presently.Suifice it to say at this time that the lower end of arm 53 is forcedforwardly by the cam so as to cause the member 52 to pivot in acounter-clockwise direction on the shaft 28. Thus the integral arm 54thereof is 9. moved upwardly carrying with it the pawl 55, it beingunderstood. that a stop pin 53 propels the pawl out of engagement withthe notch in the geared sector 2 l9.

The shaft 33 has keyed thereto a series of cams identified as PON, P0,P3, P2, Pl, 552 and 23?. When the pawl 22s is tripped subsequent to thewinding up of the motor spring 202, the energy stored in the spring isreleased and utilized to drive the shaft 38 through one revolution. Itwill be understood that when the pawl 225 is tripped, the geared sectorH9 is still locked by the latching pawl 55 so that the pinion 4i and itsintegrally-formed ratchet wheel 32 and the disc 43 are held stationaryso as to permit the energy stored in the motor spring 2 32 to beexpended in driving the shaft 38 to which the above-identified cams arepinned. Mounted on the bracket 23 in cooperative association with thecams PON, P0, P3, P2 and PI are the contact springs SON, S0, S3, S2 andSi, respectively. As described in connection with the schematic showingof the code transmitter in Fig. '7, and as will appear more fully in thecircuit description to be made hereinafter, the cams function duringtheir rotation to actuate their corresponding contact springs.

The cam 234i is provided on its peripheral edge with a flat sectionagainst which the hat spring 236 abuts as shown in Fig. 9. Thiscam-spring combination assures the shaft coming to rest in its normalposition. The spring 236, as illustrated, is mounted on the base of thetelephone set.

The cam 52, which as shown in Fig. 5, is peripherally aligned with thearm 53 of the U -shaped member 52, is provided with a camming lobe aswhich is so positioned on the cam periph ery that it functions duringthe last one-quarter revolution of the cam shaft to actuate the arm 53and cause it to disengage the pawl 55' from the geared sector 2!!) so asto allow the latter to restore to its normal position under the actionof spring 55 which is engaged by the bracket mounted on the common bar617 with which the geared sector 2 I9 is integrally formed, when thecommon bar is actuated together with any of the code bars Al, Bl, C2,D2, E3 and F3. At 58 is shown a stop mounted on the base of thetelephone set which limits the extent to which the code bars and commonbar 6? may be moved during operation.

On the underside of the cover 2i at its top and just below the cradletines which support the telephone handset 200, is mounted a bracketrigidly fixed in position by means of screws and having two dependingarms H and i2, the first of which carries the switchhook contact springsZill. The contact springs 2M are the usual switchhook springs which areoperated to effectively include the station telephone apparatus in theline circuit when the handset is removed from its support. At its outerend the bracket arm 72 pivotally supports a lever 15 having one endinterposed between the button 266 and the stud ll associated i irregularperipheral edge, one face of which normally engages a roller 17 which isrotatably mounted on the extreme end of the lever 19. The lever '19 isformed by riveting together two projections of complemental parts 89 and8|, which together form a substantially U-shaped element having twoshort arms at its extremities which are suitably apertured to receivethe shaft 28. As shown in Fig. 5, the left end of this element, or ofthe complemental portion 85 thereof, is provided with a collar @2 whichis pinned to the shaft 2t. Also at its left end the portion Si isprovided with an integral hookshaped projection 83 which normally abutsthe tripping pawl member 60 with which the tripping pawl 22!? isintegrally formed. Thus, when the telephone handset 200 is removed fromits support, the lever 15 moves in a clockwise direction about its pivotcausing lever 79 to move similarly about the shaft 28 so that theprojection 83 of the lever acts upon the member 60 to cause the trippingpawl 220 to move out of engagement with the disc 22! thereby freeing thecam shaft 2G3 for rotation under the action of motor spring 202. Thusthe shaft 263 is rotated, carrying with it the cams PON, P0, P3, P2, PI,62 and 231, the second last of which, cam 62, functioning, as previouslydescribed, during the last quarter cycle of rotation to actuate leverarm 53 and to thereby cause the disengagement of the latch pawl 55 fromthe geared sector 2!!) to permit the sector 2!!) and itsintegrally-formed common bar 67 to restore to normal. It is to beunderstood that the motor spring 292 will be so adjusted that the energystored thereby, when the spring is wound up, is sufiicient to insure acomplete revolution ofthe cam shaft 203. As the shaft reaches its homeposition, the energy in the motor spring will be sufiiciently expendedso that the engagement of spring 236 with the flat surface of cam 23'!will insure the shaft coming to rest in its home position. The arrestingof the shaft in this position is further insured by the dropping of thestud associated with the springs SON into the home position notch in camPON. The pulsing cams Pl, P2 and P3 will have functioned during thefirst three quarters of the shaft revolution to actuate the springs SiS2 and S3 in sequence.

Fig. 3 illustrates the position of the levers l5 and 19 when the handsetbutton is half-way projected from the casing 2i. In this position thepawl 22! will have been tripped and the cam shaft 293 will have startedits cycle of rotation.

When the handset 29% is completely lifted from its mounting, therelative positions of the levers l5 and 19 will be as illustrated inFig. 4. The contour of the camming end of lever is such that the lever19 occupies the same positions with the telephone handset on its supportand with the telephone handset fully removed. This is necessary sincethe code transmitter must function to transmit code signals in responseto the removal of the handset from its support, and must also be capableof transmitting code signals with the handset already removed from itssupport inthe event it is desirable to add other stations to analready-completed connection in the case ofconierence calls. Therefore,with the lever iii in the position indicated in Fig. 4, the pawl 220will be positioned so as to reengage the tooth in disc 22! at the end ofthe rotation of the cam shaft to thereby render the transmitter operableto transmit code signals while the handset is removed from its support.

In the event that a subscriber has actuated a station-selecting buttonimproperly, that is, if button No. 2 is actuated when button No. 3, forexample, should have been actuated to initiate a desired connection,provision is made to reset the transmitter before the handset is removedfrom its support and thereby render void the original sett ng of thetransmitter. To provide for this contingency, all of the buttons mountedon the telephone set, with the exception of the reset button RE, areprovided with means for latching them in their operated positions andother means, to be described presently, are provided for restoring thetransmitter to its normal position.

As shown particularly in Figs. 2 and 3, a boss I99 depending from theunderside of the casing 2! just above the position occupied by the buttons has secured to its lower face, by screws Iiii, a plate I52. Thisplate is provided with suitable apertures through which the lower shankportions of the buttons freely pass and constitutes one of threesubstantially similar plates which are mounted in superposed relation asa unit by means of screw bolts m3 and suitably-dimensioned spacingcollars [64. The middle plate I05 is a latch plate provided at each endwith aslot I56 which permits the plate to slide longitudinally a limitedamount on the upper edges of the lower collars IM. A spring IO'I havingone end fixed to the uppermost stationary plate I68 and the other endfixed to the slidable plate I05 normally biases the latch plate to theleft, viewing Figs. 7 and 7A. Each key or button, other than resetbutton RE, is provided with a ca-mming area on its shank which serves,when any of these buttons is depressed, to move the plate I85 to theright against the action of spring IO! until the camming portion of thekey shank has passed through its corresponding hole in the latch plate,when the spring I01 functions to restore the latch plate so that theupper edge or shoulder of the camming portion of the key impingesagainst the underside of the latch plate. In this manner any of thekeys, other than reset key RE, is effectively locked in its depressedposition when manually moved thereto.

Depending from the latch plate I05 near its left end is a cam projectionI69 which is adapted to be engaged by the projection IIO, fixed to theleft end of the common bar 61, in such a manner that when the common baris restored to normal, as will be described, the projection HE! in movinupwardly engages, with a cam.- ming action, the projection I89 causingthe latch plate I05 to be moved to its unlatching position and therebyeffecting the release of the depressed button. Each button is providedwith a coil spring III which is wound around the lower shank portion ofthe button and is confined between a collar I I2 and the upper face ofthe stationary plate I32. the return of the operated code bars serves torestore the button when unlatched.

The reset button RE is of the non-locking type and is normally held inits unoperated position by the spring II I. When depressed, this keyengages the extension H2 of a substantially Z- shaped member II3 whichis pivotally mounted on the shaft H4. The shaft H 3 is carried insuitable apertures in vertical extensions of bracket 3!! and bracketII5, the latter of which is fixed to the base 20 by means of screws andcooperates with a forward extension of bracket 31 in furnishing asupport for the spring 135,

This spring together with which spring, as previously mentioned, isengaged by the common bar 6'! when the latter is actuated and serves toassist in restoring the common bar to normal. The inwardly projectingarm of the Z-shaped member H3, which is identified on the drawings bythe numeral IIG, has its inner end arcuately shaped so as to function asa cam in actuating the arm IiI, which, in'turn, is pivotally mounted onthe shaft 28. A hook-like projection i l8 extends from the underedge ofthe arm Ill and makes contact with the pawl member 68 which, aspreviously described, has integrally formed therewith the tripping pawl220.

When the reset button RE is actuated subsequent to the depression andlocking of a stationselecting button and prior to the lifting of thehandset 260 from its support, the lower face of the button RE engagesthe projection H2 and depresses it. The inwardly-projecting cam arm i Itof the Z-shaped member I I3 moves upwardly from the position shown inFig. 6 to the position shown in Fig. 6A, and in so doing, earns the armI I! in a counterclockwise direction. The hook-like projection N8 of armII'I accordingly functions to lift the tripping pawl 220 out ofengagement with the tooth of disc 22I thereby freeing the cam shaft 203and permitting it to rotate under the action of motor spring 2&2. Sincethe telephone handset is not removed from its support at this time tooperate switchhook springs 28L the operation of the code-sending springsby their respective cams does not result in the transmission of a codesignal over the line. When the code-transmitting mechanism completes itscycle, the geared sector 2H3 of the common bar 6? is released in amanner previously described and under the action of spring 66 restoresto normal position. As the bar 6'! approaches normal position, theprojection I I8 thereon engages the latch plate arm I89 to move thelatch plate I 05 to its unlatching position whereupon thepreviously-operated and locked button restores to its normal positionunder the action of its corresponding spring I i I.

The six code bars AI, BI, C2, D2, and F3 and the common bar 6? arepivotally carried on shafts I It and I20, the latter being supported insuitable apertures in an extension of bracket 3i and in the bracket I2i.Suitable collars are interposed between the code bars and their supportsto maintain them in fixedspaced relation. Each of theinwardly-projecting right-hand extensions of the code bars is providedwith an integral spring-operating projection I 22 which serves tooperate the springs A, B, C, D, E and F when the corresponding code baris actuated. ihese springs, as previously described, operate to removeshort circuits from the dry rectifiers a, b, c, d, e and 1.

Each code bar is provided with short, integral substantially verticalprojections I38 which are disposed immediately below the buttons H, 2, 3to I8 mounted on the telephone set. The number of projections I3 3 oneach code bar determined by the number of buttons which operate the codebars. As indicated in Fig. '7, code bar Al, for example, is providedwith nine spaced projections so that this code bar is actuated when anyone of buttons H, 3, 5, l, 9, II, !3, I5 and I! are depressed. In caseswhere one button func-- tions to actuate more than one code bar, theprojections I39 extending from such code bars are provided with rightangular offsets so as to render the plurality of bars operable by asingle 13 button, as shown in Figs. 2' and 3. The common bar 5! is sodisposed relative to the six code bars that it is operated whenever anyone of the code barsis depressd. In other words, the common bar 6! is.actuated. whenever any one of the buttons H, 2, 3 to it is operated.

The contact springs A, B, C, D, E and F are suitably mounted on the baseof the telephone set as clearly shown in. Fig. 5, and also in Figs. 2and ,3.

Operation of the code transmitter When it is desirable for thesubscriber at a calling station to initiate a call to another station,station No. 2 for example, the button 2 corresponding to the calledstation is depressed and then the handset 2% is removed from itssupport.

Button 2, as indicated in Fig. '7, functions to actuate a single codebar Bl, so that the code bar Bl in the position of button 2 is providedwith a projection use which is engaged by the underface of the buttonand forced inwardly. Code bar Bl is therefore depressed and causes thecommon bar til to experience a similar opera.- tion. As the common barmoves downwardly, it carries with it the projection lib (Fig. 7A.) andby virtue of the oamming action of the button the latching plate ass ismoved to the right. When the camming portion of the actuated but tonclears the corresponding hole in plate the spring lc'i functions torestore the latch plate its to its normal position, causing the pressedbutton to be locked thereby in ts operated position. The projection withcode bar Bl moves upwardly to opera springs B causing these springs toto and thereby remove the short circuit from d1 y rectiher I). Thegeared sector 2 58 associated with the common bar 6? pivots on shaf iiso that its geared end is raised. The pinion gear which meshes with thegeared sector 2E5 is therefore rotated in a counterclockwise direction.ratchet wheel 32 is similarly rotated an by virtue of the pawl 35 whichcouples the ratchet wheel E2 and the disc 53, the rotation of theratchet wheel is communicated to the disc The motor spring 2532 whichcouples the discs 3 and 22 l is wound up due to the rotation of the disc53, it being understood that the disc 22% which is pinned to shaft 233is prevented from rotation at this time by the engagement tri" ping pawl22E with the tooth thereof. ihus, incident to the depr ssion of button2, energy is stored in motor spring and rectifier con tact spr ngs F areoperated to op posiucn. When the button 2' reaches the stroke, thegeared sector 2W will have been raised to such a position that the latchpawl drops into notch 57 in the geared sector to maintain the gearedsector in its operated posh tion. Thus the geared sector 2H2 and thedepressed button 2 are locked operated.

Removal of the handset from its support permits springs 2M to operate.Through the linkage consisting of handset button the pivoted lever '55,the lever arm "id is depressed causing it and its oppositely projec ingarms and (it to pivot in a clockwise direction on shaft The member 83which is integrally formed onthe left end, viewing Fig. 5, of arm iiiaccordingly moves to cause the tripping member 63 to rotate against theaction of spring ti on shaft 2Q in a counter-clockwise direction.Tripping pawl 226 which is integral with tripping 14 member as is.accordingly moved out of engage ment with the. tooth of disc 22Ewhereupon the energy stored inmotor spring 2M is released and isexpended in causing the rotation of shaft 2&3 wi h its plurality of camsPl, P2, P3", P0, PON, 23'1 and 52.

As cam 62 nears its home position, the lobe 53 thereof acts on the lowerend of. arni causing it to move. forwardly, viewing- Figs. 2' and 3. Thearm 53, as previously described, the longer right-hand extension of thesubstantially U- shaped' member 52 whose shorter left-hand arm isindicated by the numeral 54 in the drawings. Thus, due to the cammingaction of the lobe 63 of cam 52; on the arm 53, the arm 54 also is movedforwardly, or more accurately, in a counterclockwise direction. The pin53 fixed to the arm therefore functions to lift the latchingv pawl 55from the notch 57' in the geared sector 2E9 thereby releasing the gearedsector, which, as previously stated, is integral: with the common bar6i. The spring it then functions to: restore the common bar to normaland also the actuated: code bar Bl.

As the common bar 6? returns to normal, the projection I It carriedthereby moves upwardly to engage, with a camming action, the projectionHi9 of the latch plate N35. The latch plate is thereupon moved to theright a distance sufiicient to permit the depressed button to restore tonormal under the action of its associated spring H.

Operation on conference basis When the handset 269: is completelyremoved from its support, the position of lever arm 19 relative to thatof lever i5 is shown in Fig- 4. This position of lever arm 79 is thesame as that occupied by the lever arm when the handset is on itsmounting on the telephone set as shown in Fig. 2'. Thus, subsequent tothe removal of the handset from its mounting, the mechanism controlledby lever arm 19 is in its normal condition so that when the shaft 263'completes its cycle of rotation, the tripping pawl falls into the notcheffected by the tooth on the periphery of disc 225, therebyreconditioning the transmitter for a subsequent operation while thehandset is still removed from its support.

If, after actuating the button 2, and during the time the connection tothe called station is completed, the calling subscriber desires to addanother station, station No. 3 for example, to the connection, he may doso by merely actuating button 3 corresponding to station No. 3, and

2 following it with the operation of the reset button RE. When button 3is depressed, the motor spring 262 is again wound up, it being recalledthat with the handset lifted from its support the lever arm, 19 assumesits normal position, as shown in Fig. 4, so that the tripping pawl 220reengages the tooth in disc 22! to hold the disc against rotation duringthe actuation of the button and the consequent winding up of spring 282.As in the previous case,.the geared sector is locked operated whenbutton 3 is fully depressed.

When reset button RE is then actuated, its lower face engages theprojection lit 2. causing the camrning. lever iiGto. move lever illinwardly as shown in Fig. 6A, whereupon the tripping pawl 2213 throughthey engagement of the hook-like projection MB of lever li'l and the.tripping member 68, is lifted out of engagement with the tooth of disc22! permitting the spring 292' to, function to drive the cam shaft 203through a complete revolution. The cams carried thereby function totransmit the code corresponding to station No. 3, the character of whichis determined by the open condition of springs A and D which wereactuated by code bars Al and D2, respectively, when the button 3 wasdepressed.

The reset button RE also serves to permit a subscriber to correct anerror resulting from the depression of a wrong station-selecting buttonbefore the handset is removed from its support. When a button has beendepressed erroneously and the error is detected before the handset isremoved from its support, the subscriber merely actuates the resetbutton RE which releases the code-transmitting mechanism causing it toperform a complete cycle of operation. Obviously, since the signalingcircuit is open at the lowermost contacts of springs no code impulseswill be transmitted over the line when the handset is in its position onthe telephone set. After the return to normal of the transmitter in themanner previously described, the correct station button may be actuatedand the handset removed from its mounting whereupon the correct code istransmitted over the line to efiect the selection of the called station.

Circuit operation.CaZl to private branch, exchange or central office ItWill be observed that the line L extending from station No. I normallextends to a private branch exchange or central ofiice by Way of the twoinner armatures and back contacts of relay 207, link LI and the innerupper and innermost lower armatures and back contacts of cutthroughrelay 228. Thus, to extend a call to the private branch exchange, orcentral ofiice the party at station No. I, for example, need only removethe telephone handset 200 from its support to effect the closure of thecontact springs 20 l These springs when operated to their closedpositions complete the closure of the station loop in a well-knownmanner and cause the supervisory relay 204 to operate over the closedloop.

Relay 204 completes an obvious operating circuit for the slow-to-releaserelay 205. At its left armature and front contact, relay 205 connectsground potential to conductor 56l and thence over resistance 265 andconductor 244 to the right terminals of the lower windings of relays 2,252 and 253 thereby marking all such relays through which access tostation No. I is had, busy. This removal of the telephone set at stationNo. l causes the usual line rela to operate at the exchange to bring ina call signal thereat. The call is answered at the exchange in the usualmanner. In the case of an automatic exchange dial tone would beconnected to the calling line in the well-known manner.

Should the switchhook or handset button of the telephone set at stationNo. I be accidentally, momentarily depressed at this time, no permanentloss of the exchange connection results and the calling line will beautomatically reconnected to the exchange in the following manner. Theopening of the contacts 20| incident to the accidental operation of thebutton 206 at station No. I opens the station loop causing supervisoryrelay 204 to be deenergized and to release its armature. Relay 205 beingslow-to-release remains operated and during the interval in which relay204 is deenergized, relay 20'! operates in a circuit extending fromgrounded battery, through the winding of relay 201, armature and frontcontact of relay 205, upper armature and back contact of relay 208, toground at the back contact and armature of relay 204. At its outer upperarmature and front contact, relay 20'! completes a locking circuit foritself independent of the armature and back contact of relay 204. At itsinner upper and inner lower armatures and front contacts, rela 201transfers the calling line L from the link Ll extending to the privatebranch exchange, or central office to the conductors extending to thealternating current signaling source 209.

Relays 26d and 2!! of the signal receiving and register circuit operateon alternate half cycles of current from the source 209. The operatingcircuit for relay 2H extends from the right terminal of the secondarywinding of transformer 2E2, through the rcctifiers 2E3 and 2M, windin'of relay 2H, front contact and inner lower armature of relay over thering conductor of the calling line L, over the closed loop at thecalling station to the tip conductor of line L, inner upper armature andfront contact of relay 20?, to the left terminal of the secondinding oftransformer 252. Relay 2!! thus operates on the positive half cycles ofcurrent, from the source 209. The operating circuit for rela 220 may betraced similarly except that rectifiers M5 and 2H5 are substituted forrectifiers 2M and 2H5, respectively, and the winding of relay for thewinding of relay 2. Thus relay 2H operates on the negative half cyclesfrom the source "09.

Ground potential is now extended by way of the outer upper armature ofrelay 2%! and the outer lower armature of relay 2th and their respectivefront contacts, to the innermost upper armatures and back contacts ofrelay 2!? and 258, conductor 2E9, winding of relay 208, to battcry andground. Relay 208 operates in this circuit and at its upper armature andback contact opens the locking circuit for relay 201, which relaydeenergizes and restores its armatures, reconnecting the calling line Lto the link Ll extending to the exchange. With the release of relay 22?and the consequent opening of the conductors to the signaling currentsource relays 2H) and 2H release and open the operatin circuit to relay208. Relay 203 released, the circuit is restored to the condition it wasin prior to the momentar actuation of the switchhook contacts at stationNo. i and the connection between calling station and the exchange isreestablished.

Replacement of the receiver, or handset at station No. i at thetermination of the call to the exchange interrupts the station loop inthe usual manner, causing the release of rela 204, which in turn, opensthe circuit to relay 205. The circuit is then in its normal condition.

Keyed call to station N0. 2

When call is to be initiated at the station No. i, for example, andintended for the party at station No. 2, for example, to which stationthe calling party has direct access, the stationselecting button, or keyNo. 2 allocated to the called station No. 2, is manually depressed andthe telephone handset 200 removed from its support in that sequence. Thedepression of key No. 2 at station No. causes the operation of code barB! as well as the common bar with which the geared sector 2!!) isintegrally formed as previousl described. The actuated code and commonbars are locked in their operated posi- :ca'ms P3, P2 and PI.

tions. The operation of the geared sector 2l9 causes the motor spring202 to be wound up, in the manner described, while the transmitter shaft2% is restrained from rotation due to the engagement of the pawl 220with the cam 22I which is fixed to shaft 283. The handset when removedfrom its support trips the pawl 22c and closes the switchhook contactsZEH. Upon operation of the pawl 22!], the cam shaft 2533 is caused torotate receiving the energy stored in the motor spring 202. The shaft203 makes one complete revolution.

As the cams PON and PO move out of normal positions, the alternatecontacts of springs SON function to short-circuit the telephone set andthe normal contacts serve to remove the short circuit from the codesending contacts SI, S2 and S3. The contacts SO open to maintain thesignaling circuit open, it being understood, as will appear presently,that the path for the signal impulses include the contacts SO andrequires the closure of these contacts for its completion.

Immediately upon the removal of the handset from its mounting thesprings 2M are closed to complete the closure of the station loopcircuit in the well-known manner. This loop, in this system includes thenormally closed contacts SON. Relay 2M thereupon operates from batteryat the exchange and completes an obvious operating circuit for relay205. Relay 285, operated, marks relays 2M, 2252 and 253 and all otherrelays through which station No. I is reached, busy. As the cam shaft293 starts to rotate, the contacts SON and SO are operated so that thetelephone set is short-'circuited by the alternate contacts SON and theloop circuit is now open at the contacts 'SO. During this open intervalrelay Z04 releases and with relay 295 still operated due to itsslow-'to-r'elease characteristics, relay 20'! operates as previouslydescribed and locks to ground at its own outer upper armature and 'frontcontact by way of the armature and front contact of relay 285 and theupper armature and back contact of relay 2B8. Relay 281 performs thesame functions ascribed to it hereinbefore, one of which is to connectthe signaling current source 20$) to the calling line L.

With code bar BI operated in the station set, "as described, the springcontacts B controlled thereby will be opened to remove "the shortcircuit from rectifier b. These re-ctifiers, however, as "well as "allother "rectifiers a, c, d, e, and f will remain short-circuited untilthe cam springs "S3, S2 and Si are operated "by their respective Thus,it will be noted, the code bars selectively prepare certain of therectifiers ato f, inclusive 'ioreffective use in transmi'tingcorrespondingly characterized impulses while he cams PI, P2 and P3function sequentially to take the characterized impulses and apply themto the line L.

As the cam shaft 2&3 reaches-its first position afterone' quarter of arevolution, the pulsing'lobe of cam'PI will open the springs SI 'andthestud associated withthe-springs SO will drop into the firstnotch I of'camIPO. While this condition maintains, a circuit maybe traced for theposi-- tive half cycles'from source 288, from the right .tifier b fromwhich the short circuit has been removed by the operation of code bar BIand'its associated contact B, normal closed contacts A, conductor 223,alternate contacts SON, tip conductor of line L, inner upper armatureand front contact of relay Zii'l, to the left terminal of the primary oftransformer ZIZ. It will be noted that no path exists at this time forthe "negative half cycles so that only relay 2|! operates and relay 2 Iit remains unoperated.

At its inner lower armature and front contact, relay 2II connects groundto conductor 224 to maintain relay 2B5 operated. At its inner upperarmature and front contact, relay 2II completes a circuit for the'energization of relay I+ which extends from grounded battery 225,conductor 228, winding of relay I+, conductor 221, back contacts andoutermost upper armatures o'fzrelays H8 and 2I I, inner upper armatureand front contact of relay 2'I I, to ground. Relay I operates in thiscircuit and locks to ground at the back contact and outer lower armatureofrelay 208, by way of its own left armature and front contact andconductor 229. At its outer lower armature and front contact, relay 2Hestablishes a-circuit for the upper winding of relay 2T8 which may betraced from grounded battery, upper or primary winding of relay? I8,back contacts and outer lower armatures of relays 218 and 217, to groundby way of the outer lowerlarmature and front contact of relay 2| I.Relay 218 operates partiallyat this time and connects its lower orsecondary winding in series Withits-primary winding to ground at theouter lower armature and front contact of relay 2-01. Relay :2 i8 isprevented from .full operation at this time as its secondary winding .isshort-circuited by the outer lower armature and front contact of relay2-H. .tive impulselresultingfrom theopening of pulsing springs SI whichoccurs when the shaft 1203 makes the first quarter of a completerevolution, relay I-+ is operated and locked to the relay 2El8,.asdescribed. 7

As the cam shaft 203 continues to rotate under the action of motorspring 202, the cams carried thereby :move out of their .first positions:and advance to their second positions. The stud associated with thecontact springs SO moves out is deenergized.

of the :notch I in cam PO to cause the opening of thecontact springsSG.Similarly the contacts 81 controlled by cam PI are reclosed. With theopening of thecontact springsSO the signaling circuit to the-sourceace-is opened and relay :2 Relay ZII accordingly releases its armatures.In releasing .its outer lower armature relay 2I-l removes the shortcircuit from the lower or secondary winding of relay 218 thereby,,permitting this relay to operate fully. At its three upper :armaturesrelay 218 transfers the and i leads from the first -set-of directionalrelays I+ and I-, to the second setof directional relays 12+, 2- and ii.It will be noted at this time that the first set of directional relaysconsists of but two relays while the remaining two sets-of directionalrelays each-con- SlSlls'Of three relays. This is-due to the .fact thatthe first component of eachof the possible code signals is madeupof'either a positive or-a negative current impulse and never includesboth polarities. This is apparent from the -.chart shown in Fig. 9. Thesecond and third-components however may, as shown, in the chart-eachconsist-of a positive impulse, a negative impulse,

or a icombinationcf both polarities and therefor Thus, upon thetransmission of the,.posi- 19 require three directional relays forregistering such impulses.

As the cam shaft 203 reaches its second position the stud associatedwith the springs 80 drops into the notch 2 in cam PO and simultaneouslythe pulsing lobe of cam P2 functions to separate the contact springs S2.The closure of the contacts SO reestablishes the continuity of thesignaling loop and the contacts S2, in their operated condition removethe short circuit from the second pair of rectifiers c and (1. Asneither ,of the contacts C and D has been operated by the code bar BI,the rectifiers c and d are still shortcircuited on'the transmitter sideso that both half cycles from the source 259 will traverse the signalingpath. Both relays 2 I and 2i I will therefor operate at this time. Thecircuit for relay 2H] extends from the left terminal of the secondarywinding of transformer 2I2, over the front contact and inner upperarmature of relay 2&1, tip conductor of line L, alternate contacts ofsprings SON, closed cam contacts SI, conductor 222, contacts C and D,conductor 233, closed contacts 53 and SO, ring conductor of line L,inner lower armature and front contact of relay 2531, rectifier 2I6,winding of relay ZID, rectifier 2I5, to the right terminal of thesecondary of transformer 2| 2. The circuit for relay 2 I I may be tracedfrom the right terminal of the secondary winding of transformer 2I2,rectifiers 2I3 and 2M, winding of relay 2| I, front contact and innerlower ar-- rnature of relay 2B1, ring conductor of line L,

spring contacts SO and S3, conductor 2331, contacts D and C, conductor222, spring contacts SI, alternate contacts SON, tip conductor of lineL, inner upper armature and front contact of relay 201, to the leftterminal of the secondary of transformer 2 I2.

Relay 2H1, at its inner upper armature and front contact, and relay 2|I, atits inner lower armature and front contact reconnect ground to thewinding of slow-to-release relay 2 to insure this relay being heldoperated. With both relays 2H? and 2H, operated, a circuit may be tracedfrom groundfouter upper :armature and front contact of relay 2H, frontcontact and outer lower armature of relay 2), innermost upper armatureand back contact of relay 2H, innermost upper armature and front contactof relay 258 (held operated to ground at the outer lower armature andfront contact of relay 2M), winding of relay 2:, conductor 226 togrounded battery 225. Relay 22: operates in this circuit andlocks toground on conductor 229 by way of its left armature and front contact.

At the outer upper armature and front contact of relay 2H3 and the outerlower armature and front contact of relay 2II a circuit is completedfrom ground, over the outer lower armature and back contact of relay2I'I, outer lower armature and front contact of relay 2I8, to batteryand ground, through the upper, or primary Winding of relay 2l'l. Relay2I'I partially operates in this circuit and at its inner lower armatureand front contact connects its secondary, or lower winding in serieswith its upper winding to ground at the outer lower armature and frontcontact of relay 2G1. Relay 2II does not fully operate at this timebecause its secondary winding has ground potential applied to bothterminals thereof. Thus, as a result of the transmission of the secondcomponent of the code signal relay 2: is operated and locked.

As the cam shaft 2113 continues its rotation, the cams carried therebymove out of their secrelay 201.

Relay H1, at its three upper armatures transfers the and i leads fromthe second set of directional relays 2+, 2, and 2i, to the third set ofdirectional relays 3+, 3, and 3:.

As the cam shaft 203 reaches its third position the stud associated withsprings SO falls into notch 3 of cam PO causing the reclosure of springsSO and reestablishing the continuity of the signaling circuit.Simultaneously, the pulsing lobe of cam P3 operates springs S3 causingthem to separate and to thereby remove the short circuit from the lineside of rectifiers e and I. However, since neither contact E nor F hasbeen actuated by the code bar BI, these rectifiers are stillshort-circuited on their transmitter side. Neither half wave of thealternating current is therefore blocked and both half waves traversethe now closed signaling circuit to cause the reoperation of both relays2 I 0 and 2 I I. The circuit of relay 2II is traced from the rightterminal of the secondary winding of transformer 2 I2, rectifiers 2i 3and 2 I4, winding of relay 2i I, front contact and inner lower armatureof relay 291, ring conductor of line L, contact springs SO, conductor234, contacts F and E, conductor 233, contact springs S2 and SI,alternate contacts SON. tip conductor of line L, inner upper armatureand front contact of relay 261, to the left terminal of the secondary oftransformer 2I2. The circuit for relay 2H] extends from the leftterminal of the secondary of transformer 2I2, over the front contact andinner upper armature of relay 2&1, thence over the tip conductor of lineL, alternate contacts SON, contact springs SI and S2, conductor 233,contacts E and F, conductor 234, contacts S0, to the ring conductors ofthe line, inner lower armature and front contact of relay 2Q! rectifier2I6, winding of relay ZIO, rectifier 2 I 5, to the right terminal of thesecondary winding of transformer 2I2.

With both relays 2H and 2H operated, directional relay operates in acircuit traced from grounded battery 225, conductor 226, winding ofrelay 3i, front contact and innermost lower armature of relay 2 I1,outer lower armature and front contact of relay 2 i 9, front contact andouter upper armature of relay 2II to ground. Relay 3-: operated, locksto ground on conductor 229.

It will be noted at this time that when both half waves of signalingcurrent are transmitted as the second and third components of a signalcode, not only do directional relays 2: and 3: operate, but relays 2+,2, and 3+ and 3- will operate. However, it will be observed that wheneither re ay 2+ or relay 3+ is operated the circuits to the armatures2+, 2, or 3+ and 3- are opened so that the operation of relays 2+ and 2simultaneously with relay 21-, or the operation of relays 3+ andsimultaneously with relay 3: do not complete any line connectingcircuits other than the one circuit controlled by either, or both relay2i and relay 3:. In the case just describecltherefor, though relays 2+,2-, 3+ and 3- operate, they do not functionto cffecta line circuitselection.

Relay lid-l now partially operates in a'circuit traced'from groundedbattery, upper or primary "winding of relay 235, "from contact'and outerlower armature of relay 21?, to ground byway of the outer upper armatureand front contact and the outer lower armature and front contact ofrelays 258 and 2! l, respectively. In operating, relay 235 connects itslower, or secondary windingin series with its upper, or primary windingto ground at the outer lower armature and front contact of relay 291.Relay 235 is prevented from further operation as its secondary windingis short-circuited.

When shaft 203 moves out of the third position, the contact springs SOare again separated to open the signaling circuit. Relays 2H] and 2Haccordingly, are deenergized and release their 'armatures. Upon releaseof relays 2l0 and 2H, the short circuit is removed from the secondarywinding of relay 235 whereupon this relay fully operates under controlof relay 201.

Asa, result of the transmission of the three components of the signalcode which identifies the called station No. 2, directional relays 1+,2: and Bi, are operated and locked to ground under control of relay 268.The signal code which identines station 'No. 2 is made up of threecompo- "nents, a positive impulse and two impulses of both positive andnegative polarities as indicated by"the chartinFig. 9. These componentswere "selectively derived from the source 289 by the operation of codebar B lincident to the actuation 'o'f the No. 2 key at the callingstation. The

three components weresequentially transmitted through the media ofcontact springs SI, S2 and 'S3 respectively controlled'by cams Pi, P2and P3 carried by the shaft 263.

When the shaft 2% reaches its home position, the spring 235 engages thefiat surface of cam '23! carried by the shaft 2&3. In its home posi--"tion the notch in cam PON again receives the ."stud'associated with thesprings SON to further insure the shaft coming to rest in'itshome posi-"tion and also totreconnect the calling substation to the line L and toremove the short circuit thereof which was maintained during thesignaling interval by the alternate contacts SON. Thus, the signaltransmitter and the calling station circuit are restored to normalcondition, it being understood that when the shaft 24,33 reaches its.home positionthe actuated code bar Bl is re- ..stored tonormal.position as previously described.

With directional relays l+, 2i and 3;- operated and looked under controlof relay 2% the followingcircuit is established: from ground .at thefront contact and outer lower armature of relay-2M, both armaturesandfront contacts circle-3 235, winding of busy test relay 240, rightarmature and front contact of relay l+, inner right armature andfront-contact of relay 2:, innermost right armature and front contact ofvrelay 3:, conductor 239, upper l2 winding'of relay 24!, to battery andground by way of con- "ductors 298, an and resistance 29!. Relay 2if'the called line is busy, does not operate in this circuit as'willappear from the following descrip- :tion. It will be noted that batteryfor the en- 'er'gizati'on oftheconnecting relay, such'as relay 224i isassociated with the line circuit of the called station, such as line:circuitNo. 2.

C'alle'nlfstdtion busy If the line extending to called station No. "Zisbusy the connector relay 243 associated therewith will be operated. Ifoperated, relay 243 at its outer upper armature and front contactconnects ground potential to conductor 216 and thence, by way ofresistance 3%, to the conductor 2'" which as indicated in the precedingparagraph is connected to the left terminal of the I2 winding of relay2M and to corresponding windings of similar relays associated with lineNo. 2 such as windings 32 and 4-4 of relays 332 and 348, by way ofconductor 296. Thus, with ground potential connected to both sides ofthe winding i2 of relay 26!, this relay will not operate.

The circuit previously traced as extending from the armatures of relay235 through the winding of relay B le also extends through resistance345, thermistor 2&5, winding of relay 266, to battery and ground. Thus,if the called line is busy-relays Zdll and 24%! do not operate but, inabout .3 second, the time required to heat thermistor 255 to atemperature which will permit sufficient current to traverse the windingof relay 2%, relay 2&6 operates. At its middle upper armature, re la 2%connects a source of busy tone current .3? to the calling line No. lover the ring conductor thereof.

Relay iidc is self-interrupting, thatis, whenit operates, it shunts thecombination of thermistor 2 :5 in series with the relay, with theresistance The resultingcurrent is sufficient to hold relay 2% operatedbut not. enough to hold down the resistance of the thermistor 245. Thisresistance rises in about .25 second to a value that reduces the currentthrough relay 2A5 to a value that allows the relay to release anddisconnect the busy tone from the calling line. The relay again operatesslowly through the thermistor but not quite as slowly as the originaloperate period. due to the fact that the thermistor does At the sametime that relay 24-5 connected busy tone to the calling line, itconnected ground at its outermost upper armature and front contactthrough the thermistor 248 to the lower winding of relay Afterapproximately four operations of relay 2%, the resistance of thermistor2 33 drops to the point at which sufiicient current flows through thelower winding of relay 228, way of conductor 3435, to cause relay 228 tooperate.

Relay 225 operated, extends the link Ll of line circuit No. l to batteryand ground through the windings of line relay 2 39 which relay willoperate when relay Ell! releases to extend the link L! to the linecircuit L of the calling line as will now be described.

.It will be recalled that slow-to-release relay was held operated duringthe pulsing period under the control of relay 255! or relay 2H or undercontrol of both, depending upon the code transmitted. When the codetransmitting period is terminated relay 2G5 releases and opens thelocking-circuit to relay 2-91. Relay Bill, released, connects the line Lto link Ll so that line relay'il fifi is now connected across theestablished connection and will operate over the closed line icon atstation No. i.

It to be noted at this time that the arrnature and contact arrangementof relay 267! is ,h that when relay 2537i released "the continuity ofthe and ring conductors of Eline Lfand link/Ll is reestablished beforethe outer lower armature of relay 261 removes ground potential from itsfront contact. Furthermore, relay 238 is slow to operate. Therefore whenrelay 2 59 operates it connects ground by Way of its inner lowerarmature to t-e hold conductor 265 before the ground at the outer lowerarmature and front contact of relay 23'! is removed from conductor 23%.Thus, the relays which operated on the application Of ground toconductor 23? are now held operated to ground under control of linerelay 249.

At its outer lower armature and front contact relay 2% connects groundto conductor 558, then over the front contact and middle lower armatureof relay 228, conductor 258, to battery and ground through the windingof relay 268. Relay 268 operates and at its outer lower armature andback contact opens the locking circuit for the operated directionalrelays, which relays then restore to normal.

When relay 2E? released, described, the locking circuit to relays 2H,2H, and 235 is opened and these relays restore their armatures.

If desirable, the calling party may recall station No. 2 by againdepressing the No. 2 button, followed by the depression oi the resetbutton RE, to cause the code transmitter to again transmit the codecorresponding to the called station No. 2. The circuit operations underthis condition are the same as described hereinbefore in connectionr-Iith the initiation of a call at station No. i and directed towardstation No. 2. If, on a recall, the station No. 2 is still busy, relay24% operates in the manner previously described.

Should the calling party abandon the call, line relay 249 releases whenthe handset at station No. i is restored to its mounting causing relay228 to release. Relay 2% also releases when relay 2G9 restores itsarmatures.

Completion of keyed call to station No. 2

If the called line is idle there will be no direct ground connected tothe left terminal of the |2 winding of relay E li as previouslyindicated. Under this condition relays 2 3-0 and 24! will operate in acircuit extending from grounded battery associated with the line circuitNo. 2, resistance 29%, conductors 2i"! and 29G, upper I2 winding ofrelay f, conductor 239, front contact and innermost right armature ofdirectional relay 3i, front contact and inner right armature ofdirectional relay 2:, front contact and right armature of directionalrelay lzt, winding of relay 245, front contacts and armatures of relay235, outer lower armature and front contact of relay 2G! to ground.Relay 2 38 operates immediately in this circuitand at its upper armatureand front contact connects resistance 255 in shunt with its own windingthereby increasing the flow of current in the circuit previously tracedto value sufficient to cause relay 241 to operate, At its lower armatureand back contact, rela 2% opens the operating circuit of relay 265.

With relay 24H operated, ground on conductor 236 is extended over theupper double make contacts of relay 24! to conductor 259 and resistance263 and thence in parallel to battery and ground through the upperwinding of relay 262 and the lower winding of relay 228, the latterparallel branch including conductor Relays 262 and 228 operate in thesecircuits.

The ground on conductor 239 is also extended over the upper double makecontacts and outer upper armature of relay 24! to conductor 26'! andthence over two parallel branches, one by way of conductor 2'23 and theupper winding of relay 243, and the other by way of conductor 26:, thearmature and back contact of relay 268 of line circuit No. 2, resistance269, thermistor 21B, winding of relay 2'! l, to battery and ground.Relays 243 and 258 operate in these circuits.

As a consequence of the application of ground to t e conductor 23G,connecting relay 2, cut through relays 228 and 2&3, relay 262 of linecircuit No. i and ringing relay 2?; of line circuit No. 2 are operatedand it will be described presently how these relays lock operated undercontrol of line relay 2 2-?! of line circuit No. I.

It has been described hereinbefore how, after the completion of the codetransmitting period, relay 205 releases its armature to cause relay 201to be deenergized. With relay 2E1 released, the calling line L isextended to the link Ll, so that, with relay 228 operated, as described,line relay 24!! operates over the closed line loop. Relay 2B8 operates,in the manner described hereinbefore, to release the operateddirectional relays, and relay 2G7 operated, releases relays 2H, 2l8 and235.

Relay 249 at its inner lower armature and front contact connects groundto conductor 381 to hold relay 228 opera-ted. It also connects groundover resistance 263 and conductor 25! which ground, in effect, replacesthe ground on conductor 230 so that relays 24 I, 2 23 and 2' are nowheld operated under control of relay 249 as is also relay 262.

Relay 228 at its outer upper armature and front contact connects groundpotential to conductor 56!, resistance conductor 244 and thence inmultiple to the right terminals of the lower windings of relays 24!,2'52 and 253 and of all similar relays by means of which the station No.I may be reached from all other stations of the system. In this mannerthe calling line is marked busy to all other lines of the system.Similarly, when relay 243 operates its outer upper armature. ground isextended over conductor 216, resistance 35-5, conductor Eli, and thencein multiple to the right terminals of the lower windings of relays 332and 343 and of all other similar relays by means of which the stationNo, 2 may be reached from all other stations of the system. Thus thebusy condition of the called station No. 2 is made evident.

Relay 262 of line circuit No. i, operated, opens the operating circuitto the ringing relay 254 to prevent ringing current being connected tothe calling line.

Relay 242 at its inner upper and lower armatures and front contactsconnects the tip and ring conductors 255 and 25'! of line circuit No. Ito corresponding conductors 556 and 551 of line circuit No. 2.

Relay 243 at its inner upper and innermost lower armatures and frontcontacts extends the tip and ring conductors 214 and 2'75 of linecircuit No. 2 to corresponding conductors of the called line 2L ofstation No. 2 by way of corresponding conductors of link L2.

Relay 21! operates slowly, in the circuit previously traced, owing tothe interval of time required by the thermistor 210 to heat sufficientlyto allow adequate current to pass through the winding of the relay.Relay 2H at its lower and outer upper armatures and front contactsconnects the signaling current source 2T2 to the tip and ring conductors2'5 and 21'5 towards the called station No. 2 and since relay 243 isoperated and-a. relay, corresponding to relay 201 (Fig. 12) and

